New research from a team of scientists led by Colby Assistant Professor of Geology Bess Koffman reveals that lead pollution in Denali National Park and at Arctic sites is predominantly sourced from China, despite the phasing out of leaded gasoline in that country in 2001.
The new findings, recently published in the academic journal Environmental Science & Technology, are the first assessment of changes in the composition of long-range-transported pollutants since 2001.
The research conclusively shows that China’s lead-additive ban has had little impact because of the country’s continued focus on coal-burning for energy production and extensive mining and smelting of non-ferrous metals, such as copper, nickel, lead, and zinc. In addition, lead pollution is generated through iron and steel production, cement production, waste incineration, and other industrial activities. In fact, from 2013 to 2015 emissions from these industrial activities reached an estimated 37,000 metric tons per year and accounted for 78 percent of all East Asian emissions into the North Pacific region.
Koffman and her research team collected and analyzed surface snow from various elevations in Denali National Park in Alaska in June 2016. The scientists were able to trace the pollution to its source by “fingerprinting” atmospheric particles and measuring change over time. Several Colby students contributed to the research.
Koffman’s specialty is determining the origins of atmospheric dust in ice cores using geochemical approaches. By analyzing isotope ratios in the dust, scientists can better understand how the atmosphere has responded to past climate changes. Koffman has applied isotopic “fingerprinting” approaches to dust from Alaska, New Zealand, and Antarctica.
Lead is a harmful toxin to humans and ecosystems, and exposure to high levels can result in kidney and brain damage, as well as anemia and weakness. The amount of lead deposition measured in Denali and at Arctic sites is not high enough to be considered toxic or to cause adverse effects on the snowpack or ecosystems, Koffman said. The main impacts of lead on humans, animals, and ecosystems occur at sites closer to where the emissions are produced.
“However, the value of a record from Alaska, and the Arctic more broadly, is that it can show us how the amount and composition of pollution particles have changed through time,” she said. “At ice coring sites in Greenland and Europe, measurements reveal decreases in lead deposition following the phasing out of lead additives in North America and Europe, which represents a real win for ecosystems and human health. The story from Alaska, of course, is rather the opposite. Since the phase-out of leaded gasoline, you would think lead would come down, and it did a little bit, but then it just shot back up because there are so many other industrial uses of lead. Ideally, this new paper can highlight the need to continue lead-abatement measures in China.”
The research is based on data through 2016, so it’s possible that lead emissions have decreased since then, Koffman said. Future ice cores from Denali National Park will reveal how the history of Asian industrial pollution unfolds.
Other key findings:
- High-elevation and high-latitude regions in northwestern North America receive a significant portion (35–75 percent) of their dust from the deserts of China and Mongolia. However, particle compositions indicate that mineral dust is only a minor source of lead to these remote sites.
- Using data from the Denali ice core, Koffman and her team found that high elevations in Alaska receive up to 80 percent of their lead from pollution sources. Lead deposition in Alaska now equals that in southern Greenland during peak lead emissions from North America in the mid-late 20th century.
- The research also establishes new lead emissions estimates for China, Japan, Korea, and Russia, which show that pollution particles from China account for the largest portion of the pollution lead deposited in Denali National Park and at Arctic sites, up to 64 percent. Chinese pollutants account for about 50 percent of lead deposited recently in Greenland. The samples document pervasive deposition of Chinese pollutants across the western Arctic.
Lena Hanschka ’21 went to Denali in summer 2019 to collect samples for Koffman’s ongoing research and helped process previous samples collected in 2016 that were used in the research for the paper. An anthropology major, Hanschka said she became interested in Koffman’s research after taking a paleoclimate course during her sophomore year.
She applied to be a research assistant, and Koffman offered her the chance to go to Denali with two graduate students from Dartmouth College. They climbed to about 15,000 feet, traversing the terrain on backcountry skis while pulling sleds laden with equipment and gear.
“It was an absolutely incredible experience,” said Hanschka, who will soon begin a job working for the Appalachian Mountain Club. “There we were, these three young scientists working on these glaciers collecting samples at high elevations. We carried all our food, tents, and clothing, but also hundreds of pounds of scientific equipment. It was remote, extreme, and harsh—and amazing.”
Her field work in Alaska and her work in the labs at Colby directly related to her anthropological studies. “It helped me think about how so many things have an impact on human societies. Wind patterns and dust affect people all over the world,” said Hanschka. “You can zoom out and take a macro look at the world as a whole, or you can zoom in and be very micro to understand the world right around you. The geological world and the human-socio world are directly connected.”
Roujia Zhong ’22 contributed her expertise in computer science and environmental studies. Her job was to apply a statistical model to help interpret the data collected in the field. In part because of her work on the project, Zhong is pursuing her master’s degree in environmental engineering at Stanford University.
“I am particularly interested in applying machine-learning algorithms to understand environmental issues,” she said. “Working with Bess made me realize the powerful role of those models in understanding pollution sources and, broadly speaking, different environmental issues.”
Funding for the research was provided by Colby’s Buck Lab for Climate and Environment, Dartmouth College, Columbia University, and the American Association of University Women.
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